Problem: $\dfrac{3}{10} - \dfrac{5}{12} = {?}$
Answer: $ = {\dfrac{3 \times 6}{10 \times 6}} - {\dfrac{5 \times 5}{12 \times 5}} $ $ = {\dfrac{18}{60}} - {\dfrac{25}{60}} $ $ = \dfrac{{18} - {25}}{60} $ $ = -\dfrac{7}{60}$